Firefly and PC GAMESS-related discussion club

Such a modification is allowed. The point I was trying to make is that BH&HLYP can actually be considered as a version of B3LYP with HFX set to 0.5 (the only difference being that B3LYP uses a small 'excess' of local exchange and local correlation while BH&HLYP doesn't).

>Thanks very much for your reply. Indeed, the BHHLYP functional has been used a lot in TDDFT calculations. Is seems to make the charge-transfer states higher in energy indeed. In fact, it makes overestimate of such states in energy quite much, at least in my case. On the other hand, if I increase the weight of HF-exchange in the B3LYP functional from 0.2 to 0.3 (using the HFX option in Firefly) I reproduce the results for the charge-transfer states obtained with an ab-initio (CC2) method. The question is/was if such a kind of modification of B3LYP is "allowed" and might have been used before?

>>>I wonder if one can use the option HFX, to increase the weight of exact HF-exchange in a hybrid functional (B3LYP), to "remedy" the problem with charge-transfer states in TDDFT calculations. I would appreciate very much a reference to some works where this was used.